1. Field of the Invention
The present invention relates to a microwave transmitter/receiver module that operates in microwave frequency bands involving centimeter waves and millimeter waves.
2. Description of the Related Art
FIGS. 1A and 1B are a perspective view and a block diagram showing a microwave transmitter module according to a prior art operating in microwave bands around 10 GHz or over including sub-millimeter and millimeter bands.
The module has a semiconductor chip 71a serving as an oscillator (OSC), a semiconductor chip 71b serving as a modulator (MOD), and a semiconductor chip 71c serving as a power amplifier (PA). Each of the chips has a square shape of about 2 mm.times.2 mm. The chips 71a to 71c are housed in separate chambers and are shielded by a package 75 from external electromagnetic fields. The chips 71a to 71c are connected to one another through microwave transmission lines such as coaxial lines and microstrip lines.
This kind of structure is employed not only for transmitter modules but also for receiver modules having low-noise high-frequency amplifiers (LNAs) and demodulators.
Accommodating the chips 71a to 71c in three separate chambers as shown in FIG. 1A complicates the structure of the package. It is preferable to package all of the chips 71a to 71b in a single chamber and shield them from external electromagnetic fields. The package with a single chamber to accommodate and shield all chips, however, unavoidably has a large space to easily cause a cavity resonance.
To solve the problem of cavity resonance, the applicant of the present invention has proposed a microwave transmitter/receiver (T/R) module in Japanese Patent Application No. 8-180846. This module is shown in FIGS. 2A and 2B. The module has a single closed space that contains transmitter and receiver antenna patterns, etc., to provide functions necessary for microwave communication. The closed space has a narrowed space 90.
A semiconductor chip 85 is mounted on a circuit board 82, which is housed in a housing 84 made of a conductor. I/O terminals 88 electrically connecting between the chip 85 and the outside are arranged on side walls at central part of the housing 84 where the narrowed space 90 is present. The housing 84 is covered with a lid 81. A conductor layer 86 is formed at central part of the bottom surface of the lid 81. The narrowed space 90 is an electromagnetically narrowed space defined by three conductor planes consisting of the bottom and two side faces of the narrowed space 90 and one plane consisting of the conductor layer 86 at bottom of the lid 81. The board 82 further has receiver antenna patterns 83, transmitter antenna patterns 87, and feeders 89b and 89a for connecting the antenna patterns 83 and 87 to the chip 85.
FIG. 2B is a sectional view taken along a line III--III of FIG. 2A, showing part of the board 82. The board 82 consists of a first insulation layer or substrate 94, a conductive ground layer 93 formed on the insulation layer 94, and a second insulation layer 92 formed on the ground layer 93. The feeder 89a is formed on the second insulation layer 92 and is connected to the chip 85 through a bump 91.
The electromagnetically narrowed space 90 forms a waveguide. The waveguide has a cutoff frequency that is designed to be higher than a carrier frequency for microwave communication, to avoid the problem of cavity resonance and realize a compact module.
This module has the following problems:
(a) The housing 84 affects the antenna patterns 83 and 87, and therefore, the antenna patterns 83 and 87 must sufficiently be separated from the housing 84. This increases the size of the module and elongates the feeders 89b and 89a between the antenna patterns 83 and 87 and the chip 85, to increase feeder losses. PA1 (b) The lid 81 also affects the antenna patterns 83 and 87. The lid 81 must be thick to provide a sufficient mechanical strength to protect the inside of the module. This, however, increases electromagnetic radiation losses.
In this way, the microwave T/R module of FIGS. 2A and 2B has the problem of large size to secure the performance of the antenna patterns and the problem of electromagnetic radiation losses and feeder losses.